Amino-halogenophenyl alkyl thioethers are intermediates for the preparation of crop protection compositions (see, e.g., EP-A 306,222).
Under the conditions of a catalytic hydrogenation, it is expected that the feed materials undergo elimination of halogen atoms and alkylmercapto groups (see, e.g., Chem. Ind. 53, 103-109 (1994) and Comparative Example 1).
A discontinuous process for the preparation of 2-amino-6-chlorophenyl alkyl thioethers by catalytic hydrogenation using a Raney nickel catalyst is known (see DE-A 1,943,475). The selectivity which is achieved with this discontinuous process does, however, deteriorate significantly when attempts are made to carry it out continuously (see Comparative Example 1). The increasing elimination of chlorine and alkylmercapto groups also leads to a premature loss in activity of the Raney nickel catalyst, meaning that in a continuous process it has to be replaced more frequently, which would require additional expenditure.
We have now found a process for the preparation of amino-halogenophenyl alkyl thioethers by catalytic reduction of the corresponding nitro compounds which is characterized in that the nitro compound is continuously hydrogenated with hydrogen in the presence of a supported noble-metal catalyst.